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| United States Patent |
6,058,006
|
|
Yoshioka
, et al.
|
May 2, 2000
|
Electrolytic capacitor
Abstract
Disclosed is an electrolytic capacitor comprising a capacitor element
formed by winding an anode foil having pits with a diameter of not less
than 0.1 .mu.m formed on the surface thereof and a cathode foil with a
separator provided interposed therebetween, the separator having been
coated with PVA which is then dried, the capacitor element being in
contact with an electrolytic solution for electrolytic capacitor
containing ethylene glycol, whereby the electrolytic solution is gelled.
An electrolytic capacitor which comprises a capacitor element formed by
winding an anode foil and a cathode foil with a separator provided
interposed therebetween, the separator having been prepared by mixing
filament fibers formed by extruding PVA solution into a gas, the capacitor
element being impregnated with an electrolytic solution, is also
disclosed. An electrolytic capacitor which is prepared by a process which
comprises impregnating a capacitor element formed by winding an anode
foil, a cathode foil and a separator with a driving electrolytic solution,
inserting the capacitor element into an outer case, sealing the opening of
the outer case with a sealing member, and then subjecting the anode to
reformation, wherein the driving electrolytic solution contains boric acid
and a polyvinyl alcohol is attached to at least both the upper and lower
end faces of the capacitor element, is further disclosed. Proper selection
of the form of PVA in the electrolytic capacitor of the present invention
allows PVA dissolved in the electrolytic solution to effectively act on
the electrode foil, making it possible to improve the withstand voltage
and overvoltage resistance without raising the dielectric loss of the
electrolytic capacitor.
| Inventors:
|
Yoshioka; Toshikiyo (Tokyo, JP);
Shimizu; Makoto (Tokyo, JP);
Itoh; Takato (Tokyo, JP)
|
| Assignee:
|
Nippon Chemi-Con Corporation (Tokyo, JP)
|
| Appl. No.:
|
131679 |
| Filed:
|
August 10, 1998 |
Foreign Application Priority Data
| Oct 03, 1997[JP] | 9-287773 |
| Mar 27, 1998[JP] | 10-100228 |
| Apr 24, 1998[JP] | 10-131243 |
| May 28, 1998[JP] | 10-164328 |
| Jul 02, 1998[JP] | 10-202790 |
| Current U.S. Class: |
361/511; 252/62.2; 361/512; 361/518; 361/530; 361/536 |
| Intern'l Class: |
H01G 009/02; H01G 004/32 |
| Field of Search: |
361/502,504,506,511,512,517-519,530,535-537
29/25.03
252/62.2
|
References Cited
U.S. Patent Documents
| 4480290 | Oct., 1984 | Constanti et al. | 361/502.
|
| 4888666 | Dec., 1989 | Naitoh et al. | 361/512.
|
| 5055974 | Oct., 1991 | Washio et al. | 361/527.
|
| 5057972 | Oct., 1991 | Ishii | 361/512.
|
| 5661629 | Aug., 1997 | MacFarlane et al. | 361/505.
|
Primary Examiner: Kincaid; Kristine
Assistant Examiner: Dinkins; Anthony
Attorney, Agent or Firm: Sughrue, Mion, Zinn Macpeak & Seas, PLLC
Claims
What is claimed is:
1. An electrolytic capacitor, comprising a capacitor element formed by
winding an anode foil having pits with a diameter of not less than 0.1
.mu.m formed on the surface thereof and a cathode foil with a separator
provided interposed therebetween, said separator having been coated with a
polyvinyl alcohol which is then dried, said capacitor element being in
contact with an electrolytic solution for electrolytic capacitor
containing ethylene glycol, whereby said electrolytic solution is gelled.
2. The electrolytic capacitor according to claim 1, wherein said
electrolytic solution contains boric acid.
3. The electrolytic capacitor according to claim 1, wherein the amount of
polyvinyl alcohol attached to said separator is from 0.1 to 50.0
g/m.sup.2.
4. An electrolytic capacitor, comprising a capacitor element formed by
winding an anode foil and a cathode foil with a separator provided
interposed therebetween, said separator having been prepared by mixing
filament fibers formed by extruding a polyvinyl alcohol solution into a
gas, said capacitor element being impregnated with an electrolytic
solution.
5. The electrolytic capacitor according to claim 4, wherein said
electrolytic solution contains ethylene glycol and boric acid.
6. The electrolytic capacitor according to claim 4, comprising a polyvinyl
alcohol having a saponification degree of not less than 90 mol-%.
7. An electrolytic capacitor prepared by a process which comprises
impregnating a capacitor element formed by winding an anode foil, a
cathode foil and a separator with a driving electrolytic solution,
inserting said capacitor element into an outer case, sealing the opening
of said outer case with a sealing member, and then subjecting said anode
to reformation, wherein said driving electrolytic solution contains boric
acid and a polyvinyl alcohol is attached to both the upper and lower end
faces of said capacitor element.
8. The electrolytic capacitor according to claim 2, 5 or 7, wherein the
content of boric acid is from 0.1 to 40 wt-%.
9. The electrolytic capacitor according to claim 8, wherein said
electrolytic solution contains a dicarboxylic acid having side chains,
derivative thereof or salt thereof in an amount of from 0.1 to 35 wt-%.
10. The electrolytic capacitor according to claim 9, wherein the content of
said dicarboxylic acid having side chains, derivative thereof or salt
thereof is from 0.5 to 3 wt-% and the content of boric acid is from 5 to
40 wt-%.
11. The electrolytic capacitor according to claim 9, wherein the content of
said dicarboxylic acid having side chains, derivative thereof or salt
thereof is from 5 to 25 wt-% and the content of boric acid is from 0.1 to
5 wt-%.
12. The electrolytic capacitor according to claim 8, wherein said
electrolytic solution contains a C.sub.6-10 straight-chain aliphatic
saturated dicarboxylic acid, aromatic monocarboxylic acid or salt thereof
in an amount of from 0.1 to 35 wt-%.
Description
FIELD OF THE INVENTION
The present invention relates to an electrolytic capacitor and more
particularly to an electrolytic capacitor for middle and high voltage.
BACKGROUND OF THE INVENTION
An electrolytic capacitor has a small size and a large capacitance, can be
produced at a low cost and exhibits excellent properties in smoothening of
rectified output. It is one of important elements constituting various
electric and electronic devices.
In general, an electrolytic capacitor comprises as an anode a so-called
valve metal such as aluminum and tantalum having an oxide layer formed
thereon as a dielectric layer. A cathode is disposed opposed to the anode
with a separator provided interposed therebetween. An electrolytic
solution is held in the separator.
The formed foil which acts as anode is prepared by etching a foil made of a
high purity valve metal to increase the surface area thereof, and then
applying a voltage to the foil in an electrolytic solution to form an
oxide layer thereon. The withstand voltage of the oxide layer as
dielectric material is determined by the voltage applied during the
formation. The cathode foil as cathode is made of an etched high purity
foil.
The separator prevents the anode and the cathode from being short-circuited
to each other and holds an electrolytic solution. As the separator there
is used a thin low density paper such as kraft paper and manila paper.
The anode foil having a tab connected thereto and the cathode foil having a
tab connected thereto are then laminated with the separator provided
interposed therebetween. The laminate is then wound to prepare a capacitor
element. The capacitor element is then impregnated with an electrolytic
solution. The capacitor element is inserted into a case which is then
hermetically sealed. The anode foil is then subjected to reformation to
prepare an electrolytic capacitor.
As previously mentioned, the electrolytic solution for electrolytic
capacitor is brought into direct contact with the dielectric layer to act
as a true cathode. In other words, the electrolytic solution is provided
interposed between the dielectric material and the collector cathode in
the electrolytic capacitor. This means that the resistivity of the
electrolytic solution is inserted in series with the electrolytic
capacitor. Accordingly, the electrical conductivity of the electrolytic
solution has an effect on the magnitude of the dielectric loss of the
capacitor. The voltage at which the aluminum foil undergoes
shortcircuiting in the electrolytic solution is called sparking voltage of
electrolytic solution. It indicates the oxide film-forming properties of
electrolytic solution.
Boric acid and organic dicarboxylic acids such as sebacic acid and azelaic
acid have heretofore been used as electrolytic solutions for middle and
high voltage because they can provide a relatively high sparking voltage.
In some cases, butyloctanedioic acid, which provides a high sparking
voltage and exhibits a high electrical conductivity, is used as a solute
(JP-B-60-13296 (The term "JP-B" as used herein means an "examined Japanese
patent publication")). In some recent cases, 1,7-octanedicarboxylic acid
is used (JP-A-2-224217 (The term "JP-A" as used herein means an
"unexamined published Japanese patent application")).
However, in recent years, electronic apparatus comprising a switching power
supply have been widely used in the home. Thus, there is a growing demand
for the safety of electrolytic capacitors. In other words, the switching
power supply incorporated in these electronic apparatus comprises an
electrolytic capacitor. In a working atmosphere where the electric power
supplied is unstable, an excess voltage may be applied to the electrolytic
capacitor. Thus, there is a growing demand for a high safety electrolytic
capacitor which can withstand the excess voltage. However, electrolytic
capacitors comprising an electrolytic solution as previously mentioned
cannot meet this demand. It has thus been desired to provide electrolytic
capacitors having a higher withstand voltage and overvoltage resistance.
Further, electronic apparatus such as invertor having an improved
efficiency have been demanded. To this end, these apparatus have been able
to operate at a higher frequency. In order to cope with this tendency, the
electrolytic capacitors used must accordingly operate at a higher
frequency. The electrolytic capacitors comprising an electrolytic solution
as previously mentioned cannot meet this demand, too. It has thus been
desired to provide electrolytic capacitors having a lower dielectric loss.
SUMMARY OF THE INVENTION
It is therefore a first object of the present invention to provide an
electrolytic capacitor for middle and high voltage which exhibits higher
withstand voltage characteristics and overvoltage resistance. It is a
second object of the present invention to provide an electrolytic
capacitor for middle and high voltage which exhibits a lower dielectric
loss.
The first aspect of the present invention concerns an electrolytic
capacitor, comprising a capacitor element formed by winding an anode foil
having pits with a diameter of not less than 0.1 .mu.m formed on the
surface thereof and a cathode foil with a separator provided interposed
therebetween, said separator having been coated with a polyvinyl alcohol
which is then dried, said capacitor element being in contact with an
electrolytic solution for electrolytic capacitor containing ethylene
glycol, whereby said electrolytic solution is gelled.
In the foregoing electrolytic capacitor, the electrolytic solution contains
boric acid.
In the foregoing electrolytic capacitor, the amount of polyvinyl alcohol
attached to said separator is from 0.1 to 50.0 g/m.sup.2.
The second aspect of the present invention concerns an electrolytic
capacitor, comprising a capacitor element formed by winding an anode foil
and a cathode foil with a separator provided interposed therebetween, said
separator having been prepared by mixing filament fibers formed by
extruding a polyvinyl alcohol into a gas, said capacitor element being
impregnated with an electrolytic solution.
In the foregoing electrolytic capacitor, the electrolytic solution contains
ethylene glycol and boric acid.
In the foregoing electrolytic capacitor, a polyvinyl alcohol having a
saponification degree of not less than 90 mol-% is used.
The third aspect of the present invention concerns an electrolytic
capacitor prepared by a process which comprises impregnating a capacitor
element formed by winding an anode foil, a cathode foil and a separator
with a driving electrolytic solution, inserting said capacitor element
into an outer case, sealing the opening of said outer case with a sealing
member, and then subjecting said anode to reformation, wherein said
driving electrolytic solution contains boric acid and a polyvinyl alcohol
is attached to both the upper and lower end faces of said capacitor
element.
In the electrolytic capacitor according to the first, second and third
aspects of the present invention comprising an electrolytic solution
containing boric acid, the content of boric acid is from 0.1 to 40 wt-%.
In the electrolytic capacitor according to the first, second and third
aspects of the present invention comprising an electrolytic solution
containing boric acid, the electrolytic solution contains a dicarboxylic
acid having side chains, derivative thereof or salt thereof in an amount
of from 0.1 to 35 wt-%.
In the foregoing electrolytic capacitor, the content of said dicarboxylic
acid having side chains, derivative thereof or salt thereof is from 0.5 to
3 wt-% and the content of boric acid is from 5 to 40 wt-%.
In the foregoing electrolytic capacitor, the content of said dicarboxylic
acid having side chains, derivative thereof or salt thereof is from 5 to
25 wt-% and the content of boric acid is from 0.1 to 5 wt-%.
In the electrolytic capacitor according to the first, second and third
aspects of the present invention comprising an electrolytic solution
containing boric acid, the electrolytic solution contains a C.sub.6-10
straight-chain aliphatic saturated dicarboxylic acid, aromatic
monocarboxylic acid or salt thereof in an amount of from 0.1 to 35 wt-%.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a sectional view illustrating an embodiment of the present
invention;
FIG. 2 is a sectional view illustrating another embodiment of the present
invention;
FIG. 3 is a sectional view illustrating a further embodiment of the present
invention;
FIG. 4 is a diagram illustrating the structure of a capacitor element; and
FIG. 5 is a sectional view illustrating a conventional example.
DETAILED DESCRIPTION OF THE INVENTION
The electrolytic capacitor according to the first aspect of the present
invention will be further described hereinafter.
The separator to be incorporated in the electrolytic capacitor according to
the present invention has been coated with a polyvinyl alcohol
(hereinafter referred to as "PVA") solution which is then dried so that it
is attached thereto. The application of PVA solution to the separator can
be normally accomplished by applying PVA solution to the surface of the
separator using a comma reverse coating machine. Alternatively, the
separator may be dipped in PVA solution so that PVA solution is applied
thereto. The separator thus coated with PVA solution is then dried. PVA
solution thus applied then penetrates into the separator. After dried, PVA
is provided between the fibers of the separator and attached to the fibers
(hereinafter referred to as "PVA-coated paper").
As the separator there may be used nonwoven fabric, manila paper, kraft
paper, cellulose paper or the like. Alternatively, a separator made of
synthetic high molecular fibers may be used. The density of the separator
is from 0.15 to 0.9 g/cm.sup.3, preferably from 0.15 to 0.65 g/cm.sup.3.
If the density of the separator falls below this range, the resulting
separator exhibits a deteriorated strength. On the contrary, if the
density of the separator exceeds this range, the resulting capacitor
exhibits great tan .delta. (dielectric loss). The thickness of the
separator is from 20 to 150 .mu.m, preferably from 20 to 80 .mu.m. If the
thickness of the separator falls below this range, the resulting separator
exhibits a deteriorated strength. On the contrary, if the thickness of the
separator exceeds this range, the resulting capacitor exhibits great tan
.delta..
As PVA to be attached to the separator there may be used a commercially
available PVA. The polymerization degree of PVA is from 200 to 3,500.
Referring to saponification degree, PVA having a saponification degree
ranging from partially-saponified products having a saponification degree
of 70 mol-% to fully saponified products having a saponification degree of
not less than 99.5 mol-% may be used. The saponification degree of PVA is
preferably not less than 90 mol-%.
As the anode foil there is used one prepared as follows. A metal foil for
electrolytic capacitor is subjected to electrolysis in an acidic solution
to form pits on the surface thereof. The metal foil is then subjected to
etching by chemical dissolution in a high temperature acidic solution to
increase the diameter of pits and hence the surface area thereof. The
metal foil thus etched is then pre-treated. A voltage is then applied to
the metal foil in an aqueous solution of an acid such as boric acid and
phosphoric acid or salt thereof until it reaches a predetermined value.
The predetermined voltage is kept for a predetermined period of time. The
metal foil is subjected to depolarization treatment. A voltage is then
again applied to the metal foil to form a dielectric oxide layer thereon.
During this procedure, an oxide layer is formed on the surface of the
metal foil enlarged by etching. Similarly, an oxide layer is formed inside
the pits. Accordingly, the diameter of the pits in the anode foil on which
an oxide layer has been formed is smaller than that of the pits in the
metal foil which has been etched. In the present invention, an anodized
anode foil having pits with a diameter of not less than 0.1 .mu.m formed
therein is used.
As the cathode foil to be used in the present invention there may be used a
foil made of a metal such as aluminum for use in ordinary electrolytic
capacitors.
The foregoing anode foil and cathode foil are then wound with the separator
provided interposed therebetween to prepare a capacitor element. The
capacitor element thus prepared is then impregnated with an electrolytic
solution. The capacitor element thus treated is inserted into a case which
is then hermetically sealed with a sealing member.
In the present invention, PVA attached to the separator comes in contact
with the electrolytic solution which has impregnated in the pits in the
anode foil to cause the electrolytic solution to be gelled with ethylene
glycol in the electrolytic solution. Since the diameter of the pits on the
surface of the anode foil is not less than 0.1 .mu.m, there are voids wide
enough for the gel to enter deep into the pits. Accordingly, PVA can
penetrate deep into the pits to form a gel having a good adhesivity to the
dielectric layer. Thus, PVA can be uniformly mixed with the electrolytic
solution in the form of gel to provide an electrolyte having a high
sparking voltage that enhances the withstand voltage of the resulting
electrolytic capacitor. In this arrangement, the resulting electrolyte
exhibits a large contact area and a good adhesivity with respect to the
dielectric layer. Thus, the resulting electrolytic capacitor shows no rise
dielectric loss.
The behavior of the foregoing gelation can be presumed as follows. When the
capacitor element according to the present invention is brought into
contact with the electrolytic solution, the electrolytic solution
penetrates into the pits in the anode foil. Thereafter, PVA attached to
the separator comes in contact with the electrolytic solution held in the
pits so that gelation by ethylene glycol in the electrolytic solution and
PVA proceeds to obtain a gelled electrolyte having a good adhesivity to
the dielectric film. In this case, if the diameter of the pits is not less
than 0.1 .mu.m, a good gel is formed inside the pits. In this arrangement,
an electrolyte having a high sparking voltage and a good adhesivity to the
dielectric material can be obtained. Thus, an electrolytic capacitor
having a high withstand voltage and a low dielectric loss can be obtained.
In accordance with this method, the gelation by the electrolytic solution
and PVA proceeds in a good state to form a uniform dispersion of PVA in
the electrolyte. Probably because of the action of PVA, the resulting
electrolytic capacitor exhibits improved overvoltage resistance. If the
electrolytic solution contains boric acid, better gelation can be
provided, further improving overvoltage resistance.
It is also thought that the rest of PVA which has been left undissolved and
unreacted in the electrolytic solution is present between the main fibers
of the separator and attached to the main fibers, and the comprehensive
state in which the electrolytic solution is held in the separator having
PVA attached to its main fibers maintains a high electrical conductivity.
If PVA having a saponification degree of not less than 90 mol-% is used, a
higher withstand voltage can be obtained.
This is probably because if PVA solution is applied and dried, PVA solution
which has been applied penetrates into the separator, and PVA, after
dried, is uniformly attached between the fibers of the separator.
If the capacitor element is impregnated with an electrolytic solution
having PVA incorporated therein, inserted into a case which is then
hermetically sealed, and then heated to cause the electrolytic solution to
be gelled, the withstand voltage characteristics, overvoltage resistance,
etc. cannot be so improved, and the dielectric loss is raised. This is
probably because the electrolytic solution is not fairly gelled, and the
electrolytic solution which has been gelled doesn't adhere to the
dielectric film in a good state.
The electrolytic capacitor according to the second aspect of the present
invention will be further described hereinafter.
The separator to be incorporated in the electrolytic capacitor of the
present invention is prepared as follows. PVA solution is subjected to
so-called dry spinning to form PVA fibers. In some detail, PVA solution is
extruded into an inert gas or air through a fine spinneret so that it is
spun while the solvent is being diffused into the inert gas or air to form
a filament yarn which is then wound. In an ordinary drying spinning
process, the filament yarn is then drawn and heat-treated. However, this
treatment is not effected in the present invention. (The separator thus
formed will be hereinafter referred to as "separator formed by mixing PVA
fibers")
The aqueous solution of PVA used herein has a concentration of from 30 to
40%. It is preferred that PVA solution be spun in hot air. PVA to be used
herein may have a polymerization degree of from 400 to 3,500. Referring to
saponification degree, PVA having a commonly used saponification degree
ranging from partially-saponified products having a saponification degree
of about 70 mol-% to fully-saponified products having a saponification
degree of not less than 99 mol-% may be used. Preferably, PVA having a
saponification degree of not less than 90 mol-% is used.
Subsequently, in order to produce the main fibers of the separator, a pulp
of Manila hemp, kraft or other materials used for ordinary electrolytic
paper is subjected to treatment such as disaggregation, and then beaten.
The pulp is then mixed with the foregoing PVA fibers. The mixture is then
subjected to paper making to produce an electrolytic paper which is then
cut to provide the separator of the present invention.
The kind and CSF of the starting material pulp as main fiber of the
separator are not specifically limited. Manila hemp, sisal, kraft,
esparto, hemp or mixture may be used.
The starting material pulp is subjected to treatment such as
disaggregation, dusting and dehydration, beaten, and then mixed with PVA
fibers. The mixing proportion of the main fiber and PVA fiber is
preferably from 95:5 to 60:40. The paper making of the mixture is
accomplished by means of cylinder paper machine, Fourdrinier paper
machine, combination thereof or the like.
The density of the separator is from 0.15 to 0.9 g/cm.sup.3, preferably
from 0.15 to 0.65 g/cm.sup.3. If the density of the separator falls below
the above defined range, the resulting separator exhibits an insufficient
strength. On the contrary, if the density of the separator exceeds the
above defined range, the resulting electrolytic capacitor exhibits a
raised tan .delta. value. The thickness of the separator is from 20 to 150
.mu.m, preferably from 20 to 80 .mu.m. If the thickness of the separator
falls below the above defined range, the resulting separator exhibits an
insufficient strength. On the contrary, if the thickness of the separator
exceeds the above defined range, the resulting electrolytic capacitor
exhibits a raised tan .delta. value.
The anode foil and the cathode foil are then wound with the foregoing
separator provided interposed therebetween to prepare a capacitor element.
The capacitor element thus prepared is impregnated with the previously
mentioned electrolytic solution, and then inserted into an outer case
which is then hermetically sealed with a sealing material. Finally, the
capacitor element is subjected to ordinary treatment. In some detail, a
voltage is applied to the capacitor element under heating so that the
capacitor element is subjected to reformation. Thus, an electrolytic
capacitor of the present invention is prepared.
The electrolytic capacitor thus prepared exhibits a higher withstand
voltage than electrolytic capacitors comprising an ordinary electrolytic
paper free of PVA fibers of the present invention and maintains a low
dielectric loss. Further, the electrolytic capacitor thus prepared
exhibits good high-temperature durability and overvoltage resistance.
If the saponification degree of PVA to be used in the production of PVA
fibers is not less than 90 mol-%, the overvoltage resistance is further
improved.
If as the fiber to be mixed in the separator there is used a fiber obtained
by spinning from PVA solution by a method other than the method of the
present invention, e.g., ordinary vinylon, the withstand voltage is not
enhanced.
The mechanism of this phenomenon can be presumed as follows. In the present
invention, during the preparation of the electrolytic capacitor, PVA
fibers mixed in the separator of the present invention are dissolved in
and reacted with the electrolytic solution to raise the sparking voltage
of the electrolytic solution. If the electrolytic solution contains
ethylene glycol and boric acid, this reaction is accelerated, further
raising the sparking voltage of the electrolytic solution. Further, the
rest of PVA which has been left undissolved and unreacted in the
electrolytic solution is present between the main fibers of the separator
and attached to the main fibers, and the comprehensive state in which the
electrolytic solution is held in the separator having PVA attached to its
main fibers gives a high withstand voltage and overvoltage resistance and
maintains a low dielectric loss, although the reason for the mechanism is
unknown.
The electrolytic capacitor according to the third aspect of the present
invention will be further described hereinafter.
As shown in FIG. 4, an anode foil 14 having an anodized film formed on the
surface of a valve metal foil and a cathode foil 15 made of a valve metal
foil are wound with a separator 16 made of paper or the like to prepare a
capacitor element 1. The capacitor element thus prepared is inserted into
an outer case which is then hermetically sealed with a sealing member.
In the present invention, in the foregoing electrolytic capacitor, a layer
of PVA is formed on at least both the upper and lower end faces of the
capacitor element. The layer of PVA can be formed by applying or spraying
PVA onto the upper and lower end faces of the capacitor element so that it
is attached thereto. PVA to be used herein may be in any form such as
powder and fiber so far as it can form a layer on the upper and lower end
faces of the capacitor element. Further, the layer of PVA may be formed on
the side face of the capacitor element. In other words, as shown in FIG.
1, a layer of PVA (hereinafter PVA layer) 4 is formed on the end face 12
and the end face 13 of the capacitor element. Referring to the method for
forming PVA layer 4, as shown in FIG. 4, the anode foil 14 and the cathode
foil 15 are wound with the separator 16 to prepare the capacitor element 1
which is then impregnated with the foregoing electrolytic solution.
Subsequently, as shown in FIG. 1, PVA layer 4 is formed on the end face 12
and the end face 13 of the capacitor element by any method such as
coating. The capacitor element thus prepared is inserted into the outer
case 2 which is then hermetically sealed with the sealing member 3. The
capacitor element is then subjected to heat treatment. Thereafter, a
voltage is applied to the electrolytic capacitor under heating so that the
electrolytic capacitor is subjected to reformation. Thus, an electrolytic
capacitor of the present invention is prepared.
Alternatively, an electrolytic capacitor can be prepared by forming PVA
layer 4 on the end face 12 of the capacitor element 12 alone. The
capacitor element 1 thus prepared is inserted into the outer case 2 which
is then hermetically sealed with the sealing member 3. Subsequently, the
capacitor element 1 is subjected to heat treatment in such an arrangement
that the end face on which PVA layer has been formed is higher in position
than the other end face. In this case, the electrolytic capacitor is
positioned as shown in FIG. 2 during the heat treatment. Thereafter, a
voltage is applied to the electrolytic capacitor under heating so that the
electrolytic capacitor is subjected to reformation to prepare an
electrolytic capacitor according to the present invention. In FIG. 2, PVA
layer may be formed on the end face 13 which faces the inner bottom of the
outer case 2. In this case, heat treatment is effected in such an
arrangement that the position of the electrolytic capacitor is reversed
from that of FIG. 2. The electrolytic capacitor is then subjected to
reformation.
Alternatively, an electrolytic capacitor of the present invention can be
prepared by forming PVA layer 4 on the inner bottom 21 of the outer case
2. PVA layer can be formed by placing on the inner bottom 21 of the outer
case 2 the same PVA as used in the formation of PVA layer on both the two
end faces of the capacitor element. Subsequently, as shown in FIG. 4, the
capacitor element 1 prepared by winding the anode foil 14 and the cathode
foil 15 with the separator 16 is impregnated with the foregoing
electrolytic solution, and then inserted into the outer case 2 which is
then hermetically sealed with the sealing member 3. In this case, heat
treatment is effected in such an arrangement that the bottom of the outer
case faces upward, i.e., the position of the electrolytic capacitor is
reversed from that of FIG. 3. Thereafter, the electrolytic capacitor is
then subjected to reformation.
As PVA to be used herein there may be used a commercially available PVA.
Referring to saponification degree, PVA having a saponification degree
ranging from partially-saponified products having a saponification degree
of 75 mol-% to fully saponified products having a saponification degree of
not less than 99.5 mol-% may be used.
The electrolytic capacitor thus prepared exhibits a high withstand voltage
and a good overvoltage resistance and maintains a low dielectric loss.
The reason why the electrolytic capacitor of the present invention shows
such a behavior can be thought as follows. The electrolytic capacitor of
the present invention is prepared by a process which comprises inserting a
capacitor element 1 into an outer case 2 which is then hermetically sealed
with a sealing material 3, and then subjecting the capacitor element to
heat treatment so that a PVA layer is formed on both end faces 12 and 13
of the capacitor element. In other words, if a PVA layer is formed on only
one end face of the capacitor element, heat treatment is effected in such
an arrangement that the end face on which PVA layer has been formed is
positioned higher the other end face. Therefore, PVA in PVA layer thus
formed reaches the other end face of the capacitor element along the side
face of the capacitor element to form another PVA layer thereon. Further,
since the electrolytic solution of the present invention contains boric
acid, PVA in these PVA layers is dissolved in the electrolytic solution in
a good state. As a result, the electrolytic solution on both the end faces
of the capacitor element exhibits a raised sparking voltage. The foil
which acts as an anode foil for electrolytic capacitor which has been
formed is cut to the length according to the size of the capacitor
element, and then wound with a separator to prepare an electrolytic
capacitor element. Accordingly, the section of the formed foil is exposed
at both ends of the capacitor element. Since the sparking voltage of the
electrolytic solution present at these areas is raised, the withstand
voltage of the section of the formed foil, which exhibits the lowest
withstand voltage in the formed foil, can be raised by raising the
reformation voltage. As a result, the withstand voltage of the
electrolytic capacitor is raised.
Further, it is thought that when the anode foil 14 and the electrode tab 11
are connected to each other, some oxide layer comes off the anode foil.
Since there is a gap between the electrode tab and the separator 16 in the
capacitor element thus wound, PVA in the PVA layer formed on the end face
of the capacitor element is dissolved in the electrolytic solution in the
gap, raising the sparking voltage of the electrolytic solution at this
area. Thus, the withstand voltage of the area of the anode foil from which
an oxide layer has come off can be raised similarly to the section of the
formed foil. Accordingly, the withstand voltage of the entire electrolytic
capacitor can be raised.
PVA in the PVA layer formed on the end face of the capacitor element is
dissolved in the electrolytic solution on the end face of the capacitor
element. Since the amount of PVA dissolved in the electrolytic solution
contained inside the capacitor element is small enough to prevent the rise
in the electrical conductivity of the electrolytic solution, making it
possible to keep the dielectric loss of the electrolytic capacitor low.
Further, when an overvoltage is applied to the electrolytic capacitor of
the present invention, it is also applied to the anode foil which then
generates heat. This heat generation causes PVA in the PVA layer formed on
the end face of the capacitor element to be rapidly dissolved in the
electrolytic solution. This rapidly raises the sparking voltage of the
electrolytic solution. As a result, the sparking voltage exceeds the
overvoltage, inhibiting ignition. Thereafter, if the overvoltage is
continuously applied to the electrolytic capacitor, the film forming at
the oxide layer on the end faces of the capacitor element continues.
During this procedure, heat generation and gas production occur, causing
the valve of the electrolytic capacitor to open. Thereafter, the solvent
component is evaporated away from the electrolytic solution. This causes
so-called dry-up state that makes the electrolytic capacitor open.
If the electrolytic solution is free of boric acid, PVA makes the
electrolytic solution semisolid when it is dissolved therein. Thus, the
withstand voltage of the electrolytic capacitor cannot be raised.
If PVA is incorporated in the electrolytic solution to keep the withstand
voltage of the electrolytic solution high enough, the resulting
electrolytic solution exhibits a raised viscosity that makes it difficult
for itself to penetrate into the capacitor element and raises the
electrical conductivity thereof. Thus, the withstand voltage of the
electrolytic capacitor cannot be raised as high as the present invention.
The electrolytic solution will be further described hereinafter.
In the electrolytic capacitor of the present invention, the electrolytic
solution comprises boric acid incorporated therein to further improve
withstand voltage and overvoltage resistance. The content of boric acid is
from 0.1 to 40 wt-%. If the content of boric acid falls below 0.1 wt-%,
the resulting withstand voltage is lowered. On the other hand, if the
content of boric acid exceeds 40 wt-%, the resulting tan .delta. value is
raised.
The first embodiment of the electrolytic solution of the present invention
comprises a dicarboxylic acid having side chains, derivative thereof or
salt thereof incorporated therein in addition to boric acid. Examples of
the dicarboxylic acid having side chains include 1,6-decanedicarboxylic
acid, 5,6-decanedicarboxylic acid, 1,10-decanedicarboxylic acid,
1,7-octanedicarboxylic acid, 2,4,7,6-tetramethyl-1,10-decanedicarboxylic
acid, 2,4,7,9-tetramethyl-1,6-decanedicarboxylic acid,
2,4,7,6-tetramethyl-5,6-decanedicarboxylic acid, and
7-methyl-7-methoxycarbonyl-1,9-decanedicarboxylic acid. Examples of the
derivative of these dicarboxylic acids include
7,9-dimethyl-7,9-dimethoxycarbonyl-1,11-dodecanedicarboxylic acid, and
7,8-dimethyl-7,8-dimethoxycarbonyl-1,14-tetradecanedicarboxylic acid.
The content of the dicarboxylic acid having side chains, derivative thereof
or salt thereof (hereinafter referred to as "dicarboxylic acids having
side chains") in the electrolytic solution is preferably from 0.1 to 35
wt-%.
More preferably, the content of dicarboxylic acids having side chains is
from 0.5 to 3 wt-%, and the content of boric acid is from 5 to 40 wt-%. In
this case, if the content of dicarboxylic acids having side chains
deviates from the above defined range, the resulting withstand voltage is
lowered. If the content of boric acid falls below the above defined range,
the resulting withstand voltage is lowered. On the other hand, if the
content of boric acid exceeds the above defined range, the resulting tan
.delta. value is raised.
Even more preferably, the content of dicarboxylic acids having side chains
is from 5 to 25 wt-%, and the content of boric acid is from 0.1 to 5 wt-%.
In this case, if the content of dicarboxylic acids having side chains
falls below the above defined range, the resulting tan .delta. value is
raised. On the contrary, if the content of dicarboxylic acids having side
chains exceeds the above defined range, the resulting withstand voltage is
lowered. If the content of boric acid falls below the above defined range,
the resulting withstand voltage is lowered. On the other hand, if the
content of boric acid exceeds the above defined range, the resulting tan
.delta. value is raised.
The second embodiment of the electrolytic solution of the present invention
comprises a C.sub.6-10 straight-chain aliphatic dicarboxylic acid,
aromatic monocarboxylic acid or salt thereof incorporated therein in
addition to boric acid. Examples of the C.sub.6-10 straight-chain
aliphatic dicarboxylic acid include adipic acid, pimelic acid, suberic
acid, azelaic acid, and sebacic acid. Examples of the aromatic
monocarboxylic acid include benzoic acid, and toluic acid.
If the straight-chain aliphatic dicarboxylic acid has less than 6 carbon
atoms, the resulting withstand voltage is lowered. On the contrary, if the
straight-chain aliphatic dicarboxylic acid has more than 11 carbon atoms,
the resulting tan .delta. value is raised. Further, if the electrolytic
solution comprises an aromatic dicarboxylic acid incorporated therein, the
resulting withstand voltage is lowered.
The content of the C.sub.6-10 straight-chain aliphatic dicarboxylic acid,
aromatic monocarboxylic acid or salt thereof (hereinafter referred to as
"straight-chain aliphatic dicarboxylic acids") is preferably from 0.1 to
35 wt-%. If the content of straight-chain aliphatic dicarboxylic acids
falls below 0.1 wt-%, the resulting tan .delta. value is raised. On the
contrary, if the content of straight-chain aliphatic dicarboxylic acids
exceeds 35 wt-%, the resulting withstand voltage is lowered.
Examples of the salt of C.sub.6-10 straight-chain aliphatic dicarboxylic
acid or aromatic monocarboxylic acid include ammonium salt of these acids,
amine salt of these acids, quaternary ammonium salt of these acids, and
cyclic amidine compound quaternary salt of these acids. Examples of amines
constituting the amine salt include primary amine such as methylamine,
ethylamine, propylamine, butylamine and ethylenediamine, secondary amine
such as dimethylamine, diethylamine, dipropylamine, methylethylamine and
diphenylamine, and tertiary amine such as trimethylamine, triethylamine,
tripropylamine, triphenylamine and 1,8-diazabicyclo(5,4,0)-undecene-7.
Examples of quaternary ammonium constituting the quaternary ammonium salt
include tetraalkylammonium such as tetramethylammonium,
tetraethylammonium, tetrapropylammonium, tetrabutylammonium, methyl
triethylammonium and dimethyl diethylammonium, and pyridium such as
1-methylpyridium, 1-ethylpyridium, and 1, 3-diethylpyridium. Examples of
cations constituting the cyclic amidine compound quaternary salt include
cations formed by quaterizing the following compounds. Imidazole
monocyclic compounds (e.g., imidazole homologs such as 1-methylimidazole,
1,2-dimethylimidazole, 1,4-dimethyl-2-ethylimidazole and
1-phenylimidazole, oxyalkyl derivatives such as
1-methyl-2-oxymethylimidazole and 1-methyl-2-oxyethylimidazole, nitro and
amino derivatives such as 1-methyl-4(5)-nitroimidazole and
1,2-dimethyl-5(4)-aminoimidazole), benzoimidazole (e.g.,
1-methylbenzoimidazole, 1-methyl-2-benzylbenzoimidazole), compounds having
2-imidazoline ring (e.g., 1-methylimidazoline, 1,2-dimethylimidazoline,
1,2,4-trimethylimidazoline, 1,4-dimethyl-2-ethylimidazoline,
1-methyl-2-phenylimidazoline), compounds having tetrahydropyrimine ring
(e.g., 1-methyl-1,4,5,6-tetrahydropyrimidine,
1,2-dimethyl-1,4,5,6-tetrahydropyrimidine,
1,8-diazabicyclo[5.4.0]undecene-7,1, 5-diazabicyclo[4.3.0]nonene-5)
Examples of the solvent to be used herein include protonic organic polar
solvents such as monovalent alcohol (e.g., ethanol, propanol, butanol,
pentanol, hexanol, cyclobutanol, cyclopentanol, cyclohexanol, benzyl
alcohol), polyvalent alcohol and oxyalcohol compound (e.g., ethylene
glycol, propylene glycol, glycerin, methyl cellolsolve, ethyl cellosolve,
methoxy propylene glycol, dimethoxy propanol), and aprotic organic polar
solvents such as amide (e.g., N-methylformamide, N,N-dimethylformamide,
N-ethylformamide, N,N-diethylformamide, N-methylacetamide,
N,N-dimethylacetamide, N-ethylacetamide, N,N-diethylacetamide,
hexamethylphosphoric amide), lactone (e.g., .gamma.-butyrolactone,
.delta.-valerolactone, .gamma.-valerolactone), cyclic amide (e.g.,
N-methyl-2-pyrrolidone, ethylene carbonate, propylene carbonate,
isobutylene carbonate), nitrile (e.g., acetonitrile), oxide (e.g.,
dimethyl sulfoxide) and 2-imidazolidinone [e.g., 1,
3-dialkyl-2-imidazolidinone such as 1,3-dimethyl-2-imidazolidinone,
1,3-diethyl-2-imidazolidinone and 1,3-di(n-propyl)-2-imidazolidinone,
1,3,4-trialkyl-2-imidazolidinone such as
1,3,4-trimethyl-2-imidazolidione].
The electrolytic solution for electrolytic capacitor according to the
present invention can comprise a boric compound such as boric acid,
complex compound of boric acid with a polysaccharide (e.g., mannitol,
sorbitol) and complex compound of boric acid with a polyvalent alcohol
(e.g., ethylene glycol, glycerin), a surface active agent, colloidal
silica, etc. incorporated therein to further enhance the withstand
voltage. However, PVA is not incorporated in the electrolytic solution in
the present invention.
The electrolytic solution of the present invention may comprise various
additives incorporated therein for the purpose of lessening leakage
current or absorbing hydrogen gas. Examples of these additives include
aromatic nitro compounds (e.g., p-nitrobenzoic acid, p-nitrophenol),
phosphorus compounds (e.g., phosphoric acid, phosphorous acid,
polyphosphoric acid, acidic phosphoric acid ester compound), and
oxycarboxylic acid compounds.
In the electrolytic capacitor according to the first to third aspects of
the present invention, an electrolytic solution containing dicarboxylic
acids having side chains and boric acid, i.e., first embodiment of the
electrolytic solution according to the present invention, if used,
exhibits a high sparking voltage and a high electrical conductivity. The
resulting synergistic effect makes it possible to obtain an electrolytic
capacitor having a higher withstand voltage and overvoltage resistance
without impairing the dielectric loss.
In the electrolytic capacitor according to the first to third aspects of
the present invention, an electrolytic solution containing straight-chain
aliphatic dicarboxylic acids having side chains and boric acid, i.e.,
second embodiment of the electrolytic solution according to the present
invention, if used, exhibits a high electrical conductivity. The resulting
synergistic effect makes it possible to obtain an electrolytic capacitor
having a high withstand voltage suitable for use in middle and high
voltage and a low dielectric loss.
The present invention will be further described in the following examples.
Unless otherwise indicated, all the parts are by weight.
Firstly, embodiments of the electrolytic capacitor according to the first
aspect of the present invention comprising a PVA-coated separator and an
anode foil having pits with a diameter of not less than 0.1 .mu.m formed
thereon will be described.
EXAMPLE 1
An aqueous solution having PVA (saponification degree: 99 mol-%;
polymerization degree: 1,700) dissolved therein in an amount of 5% was
applied to a separator (manila paper; density: 0.25 g/cm.sup.3 ;
thickness: 40 .mu.m), and then heated and dried to obtain a separator
having PVA attached thereto. The attached amount of PVA was 10 g/m.sup.2.
A cathode foil and an anode foil which has pits with a diameter of not
less than 0.1 .mu.m formed thereon were wound with the separator provided
interposed therebetween to prepare a 400 V-10 .mu.F capacitor element.
Separately, an electrolytic solution comprising 100 parts of ethylene
glycol and 15 parts of ammonium 1,6-decanedicarboxylate was prepared. The
capacitor element thus prepared was impregnated with the electrolytic
solution, and then inserted into an aluminum case which was then
hermetically sealed with a rubber member. Subsequently, 425 V was applied
to the electrolytic capacitor at a temperature of 105.degree. C. for 3
hours so that the electrolytic capacitor was subjected to reformation. At
the same time, the electrolytic solution was gelled. Thus, an aluminum
electrolytic capacitor was prepared.
EXAMPLE 2
An aluminum electrolytic capacitor was prepared in the same manner as in
Example 1 except that as the separator there was used a kraft paper having
a density of 0.60 g/cm.sup.3 and a thickness of 20 .mu.m.
EXAMPLE 3
An aluminum electrolytic capacitor was prepared in the same manner as in
Example 1 except that as the electrolytic solution there was used one
comprising 100 parts of ethylene glycol, 15 parts of ammonium
1,6-decanedicarboxylate and 3 parts of boric acid.
EXAMPLE 4
An aluminum electrolytic capacitor was prepared in the same manner as in
Example 2 except that the amount of PVA attached to the separator was 0.05
g/m.sup.2.
COMPARATIVE EXAMPLE 1
A cathode foil and an anode foil which has pits with a diameter of not less
than 0.1 .mu.m formed thereon were wound with a separator (kraft paper;
density: 0.60 g/cm.sup.3 ; thickness: 40 .mu.m) provided interposed
therebetween to prepare a 400 V-10 .mu.F capacitor element. Separately, an
electrolytic solution comprising 100 parts of ethylene glycol and 15 parts
of ammonium 1,6-decanedicarboxylate was prepared. The capacitor element
thus prepared was impregnated with the electrolytic solution, and then
inserted into an aluminum case which was then hermetically sealed with a
rubber member. Subsequently, 425 V was applied to the electrolytic
capacitor at a temperature of 105.degree. C. for 3 hours so that the
electrolytic capacitor was subjected to reformation. Thus, an aluminum
electrolytic capacitor was prepared.
COMPARATIVE EXAMPLE 2
An aluminum electrolytic capacitor was prepared in the same manner as in
Comparative Example 1 except that as the separator there was used a kraft
paper having a density of 0.60 g/cm.sup.3 and a thickness of 20 .mu.m.
COMPARATIVE EXAMPLE 3
An aluminum electrolytic capacitor was prepared in the same manner as in
Comparative Example 1 except that as the separator there was used a manila
paper having a density of 0.25 g/cm.sup.3 and a thickness of 40 .mu.m.
COMPARATIVE EXAMPLE 4
An aluminum electrolytic capacitor was prepared in the same manner as in
Example 1 except that as the anode foil there was used one having pits
with a diameter of less than 0.1 .mu.m formed thereon.
COMPARATIVE EXAMPLE 5
An aluminum electrolytic capacitor was prepared in the same manner as in
Comparative Example 3 except that the capacitor element was impregnated
with an electrolytic solution comprising 100 parts of ethylene glycol, 15
parts of ammonium 1, 6-decanedicarboxylate and 11 parts of PVA
(saponification degree: 99 mol-%; polymerization degree: 1,700), inserted
into an aluminum case which was then hermetically sealed, and then
subjected to reformation at 425 V and 105.degree. C. for 3 hours while the
electrolytic solution was being gelled.
These aluminum electrolytic capacitors were each then subjected to
high-temperature load test at 400 V and 105.degree. C. for 2,000 hours.
The results of the test are set forth in Table 1. For the test, 20 pieces
of the electrolytic capacitor were used for each example. In order to
determine various properties, the values were averaged over 20 pieces.
TABLE 1
______________________________________
After 105.degree. C.-2000 hrs.
Initial properties
% Capacitance
Capacitance (.mu.F)
tan.delta.
change tan.delta.
______________________________________
Example 1
10.01 0.02 -0.1 0.02
Example 2 10.05 0.04 -0.1 0.04
Example 3 10.08 0.02 0.1 0.02
Example 4 10.00 0.05 -0.1 0.06
Comparative 10.01 0.05 -0.2 0.07
Example 1
Comparative 10.01 0.04 -0.4 0.07
Example 2
Comparative
Shortcircuited -- --
Example 3 during reformation
Comparative
2.15 0.09 -- --
Example 4
Comparative 1.08 0.45 -- --
Example 5
______________________________________
Table 1 shows that the prior art aluminum electrolytic capacitor of
Comparative Example 3 comprising a low density separator shows
shortcircuiting during reformation while the aluminum electrolytic
capacitors of Examples 1 and 3 comprising a low density (0.25 g/cm.sup.3)
separator show no problems in initial properties and life properties. In
other words, the electrolytic capacitors according to the present
invention exhibit an improved withstand voltage, making it possible to use
a low separator. The use of such a low density separator makes it possible
to reduce tan .delta. from that of Example 2 comprising a separator having
a usual density (0.60 g/cm.sup.3) as shown in Examples 1 and 3.
Comparative Example 4 comprising an anode foil having pits with a diameter
of less than 0.1 .mu.m formed thereon and Comparative Example 5 involving
the impregnation of the capacitor element with an electrolytic solution
containing PVA which is then gelled after capacitor assembly exhibit a low
initial capacitance and a high tan .delta. value and thus cannot provide
normal aluminum electrolytic capacitor properties.
Subsequently, the aluminum electrolytic capacitors of Examples 1 to 4 and
Comparative Examples 1 and 2 were subjected to overvoltage test at 480 V
and 500 V at a temperature of 105.degree. C. for 100 hours. The results
are set forth in Table 2. For the overvoltage test, 20 pieces of the
aluminum electrolytic capacitor were used for each example. The number of
pieces showing shortcircuiting is set forth in Table 2.
TABLE 2
______________________________________
500 V-100 hrs
480 V-1000 hrs Number of pieces
Number of pieces showing showing
Example No. shortcircuiting shortcircuiting
______________________________________
Example 1 0 3
Example 2 0 0
Example 3 0 0
Example 4 0 1
Comparative 2 --
Example 1
Comparative 4 --
Example 2
______________________________________
Table 2 shows that in 480V-100 hour overvoltage test the aluminum
electrolytic capacitors of Examples 1 to 4 show no shortcircuiting and
exhibit an improved overvoltage resistance while the prior art aluminum
electrolytic capacitor of Comparative Example 1 and the aluminum
electrolytic capacitor of Comparative Example 2 comprising a thin
separator (20 .mu.m) (Comparative Example 2) show shortcircuiting. This
means that a thin separator (20 .mu.m) can be used in the electrolytic
capacitor of the present invention as shown in Examples 2 and 4 to reduce
the capacitor size.
In 500V-100 hour overvoltage test, the electrolytic capacitor of Example 3
comprising a low density (0.25 g/cm.sup.3) separator impregnated with an
electrolytic solution containing boric acid shows no shortcircuiting while
the electrolytic capacitor of Example 1 comprising the same low density
separator impregnated with an ordinary electrolytic solution shows
shortcircuiting. This means that the incorporation of boric acid in the
electrolytic solution makes it possible to further improve the overvoltage
resistance.
The electrolytic capacitor of Example 2 comprising a separator having PVA
attached thereto in an amount of 10 g/m.sup.2 shows no shortcircuiting
while the electrolytic capacitor of Example 4 comprising a separator
having PVA attached thereto in an amount of 0.05 g/m.sup.2 shows
shortcircuiting. This means that the attached amount of PVA has an effect
on the overvoltage resistance.
Embodiments of the electrolytic capacitor according to the first aspect of
the present invention comprising a PVA-coated separator, an anode foil
having pits with a diameter of not less than 0.1 .mu.m formed thereon and
an electrolytic solution containing dicarboxylic acids having side chains
and boric acid will be described hereinafter.
EXAMPLE 5
An aqueous solution having PVA (saponification degree: 96 mol-%;
polymerization degree: 1,700) dissolved therein in an amount of 20% was
applied to a separator (kraft paper; density: 0.75 g/cm.sup.3 ; thickness:
50 .mu.m) by means of a comma reverse type coating machine, and then
heated and dried to obtain a separator having PVA attached thereto. The
attached amount of PVA was 5 g/m.sup.2. A cathode foil and an anode foil
which has pits with a diameter of not less than 0.1 .mu.m formed thereon
were then wound with the foregoing separator provided interposed
therebetween to prepare a 500V-10 .mu.F capacitor element. Separately, an
electrolytic solution comprising 100 parts of ethylene glycol, 15 parts of
ammonium 1,7-octanedicarboxylate and 3.5 parts of boric acid was prepared.
The capacitor element thus prepared was impregnated with the foregoing
electrolytic solution, inserted into an aluminum case which was then
hermetically sealed with a rubber member, and then subjected to
reformation at 550 V under heating while the electrolytic solution was
being gelled to prepare an aluminum electrolytic capacitor.
EXAMPLE 6
An aluminum electrolytic capacitor was prepared in the same manner as in
Example 5 except that as the electrolytic solution there was used one
comprising 100 parts of ethylene glycol, 15 parts of ammonium
1,6-decanedicarboxylate and 3.5 parts of boric acid.
EXAMPLE 7
An aluminum electrolytic capacitor was prepared in the same manner as in
Example 5 except that as the electrolytic solution there was used one
comprising 100 parts of ethylene glycol, 1 part of ammonium
1,6-decanedicarboxylate and 15 parts of boric acid.
COMPARATIVE EXAMPLE 6
An aluminum electrolytic capacitor was prepared in the same manner as in
Example 5 except that as the electrolytic solution there was used one
comprising 100 parts of ethylene glycol and 15 parts of ammonium
1,7-octanedicarboxylate.
COMPARATIVE EXAMPLE 7
An aluminum electrolytic capacitor was prepared in the same manner as in
Example 5 except that as the electrolytic solution there was used one
comprising 100 parts of ethylene glycol and 30 parts of boric acid.
COMPARATIVE EXAMPLE 8
An aluminum electrolytic capacitor was prepared in the same manner as in
Example 5 except that an ordinary separator was used.
CONVENTIONAL EXAMPLE 1
An aluminum electrolytic capacitor was prepared in the same manner as in
Example 5 except that an ordinary separator and an electrolytic solution
comprising 100 parts of ethylene glycol, 15 parts of ammonium
1,6-decanedicarboxylate, 3.5 parts of boric acid and 3 parts of PVA were
used.
The aluminum electrolytic capacitors of Examples 5 to 7, Comparative
Examples 6 to 8 and Conventional Example 1 were each subjected to
high-temperature load test at 500 V and 105.degree. C. for 2,000 hours.
The results are set forth in Table 3. For the high-temperature load test,
20 pieces of the electrolytic capacitor were used for each example. In
order to determine various properties, the values were averaged over 20
pieces.
TABLE 3
______________________________________
Initial properties
After 105.degree. C.-2000 hrs
Capacitance % Capacitance
(.mu.F) tan .delta. change tan .delta.
______________________________________
Example 5
9.78 0.027 -0.1 0.032
Example 6 10.03 0.028 -0.2 0.032
Example 7 10.00 0.029 -0.2 0.033
Comparative
Shortcircuited -- --
Example 6 during reformation
Comparative
9.77 0.093 0.3 0.111
Example 7
Comparative
Shortcircuited -- --
Example 8 during reformation
Conventional Shortcircuited -- --
Example 1 during reformation
______________________________________
Table 3 shows that the electrolytic capacitors of Examples 5 to 7 give good
results both in initial properties and high-temperature load test. In
other words, the synergistic effect obtained by the improvement of
withstand voltage of the electrolytic capacitor of the present invention
and the high sparking voltage and electrical conductivity of the
electrolytic solution makes it possible to improve withstand voltage
without increasing the dielectric loss. Thus, a high voltage aluminum
electrolytic capacitor having a rated voltage of 500 V was realized.
For comparison, the electrolytic capacitor of Comparative Example 6
comprising an electrolytic solution free of boric acid, the electrolytic
capacitor of Comparative Example 8 comprising an ordinary separator and
the conventional high voltage electrolytic capacitor of Conventional
Example 1 show shortcircuiting during reformation. The electrolytic
capacitor of Comparative Example 7 which comprises boric acid as a main
solute to provide a high withstand voltage shows no shortcircuiting during
reformation and high-temperature load test but exhibits a raised tan
.delta. value exceeding the maximum allowable range.
The aluminum electrolytic capacitors of Examples 5 to 7 were each subjected
to overvoltage test at 500 V and 600 V at 105.degree. C. for 50 hours. The
results of the test are set forth in Table 4. For the overvoltage test, 20
pieces of the electrolytic capacitor were used for each example. The
number of pieces showing shortcircuiting is set forth in Table 4.
TABLE 4
______________________________________
After 600 V-50 hrs
After 550 V-50 hrs Number of pieces
Number of pieces showing showing
Example No. shortcircuiting shortcircuiting
______________________________________
Example 5 0 0
Example 6 0 0
Example 7 0 0
______________________________________
Table 4 shows that the electrolytic capacitors of Examples 5 to 7 show no
shortcircuiting during 550 V and 600 V overvoltage tests and thus exhibit
a good overvoltage resistance.
Embodiments of the electrolytic capacitor according to the second aspect of
the present invention comprising a separator having PVA fibers mixed
therein and an electrolytic solution containing dicarboxylic acids having
side chains and boric acid will be described hereinafter.
EXAMPLE 8
An aqueous solution having PVA (saponification degree: 80 mol-%;
polymerization degree: 1,700) dissolved therein in an amount of 35% was
extruded into hot air through a spinneret to form a filament which was
then wound to prepare a PVA fiber. Subsequently, a hemp pulp was subjected
to disaggregation, dusting and dehydration, and then beaten. The hemp pulp
thus treated was then mixed with the foregoing PVA fiber at a ratio of
80:20. The mixture was then subjected to paper making by means of a
cylinder paper machine to prepare an electrolytic paper. The electrolytic
paper thus prepared was then cut to provide a separator. A cathode foil
and an anode foil which has pits with a diameter of not less than 0.1
.mu.m formed thereon and has a withstand voltage of 650 V were wound with
the foregoing separator provided interposed therebetween to prepare a 500
V-10 .mu.F capacitor element. Subsequently, an electrolytic solution
comprising 100 parts of ethylene glycol, 15 parts of ammonium
1,7-octanedicarboxylate and 3 parts of boric acid was prepared. The
capacitor element thus prepared was impregnated with the foregoing
electrolytic solution, inserted into an aluminum case which was then
hermetically sealed with a rubber member, and then subjected to
reformation at 550 V under heating to prepare an aluminum electrolytic
capacitor.
EXAMPLE 9
An aluminum electrolytic capacitor was prepared in the same manner as in
Example 8 except that PVA having a saponification degree of 98 mol-% was
used.
EXAMPLE 10
An aqueous solution having PVA (saponification degree: 98 mol-%;
polymerization degree: 1,700) dissolved therein in an amount of 35% was
extruded into hot air through a spinneret to form a filament which was
then wound to prepare a PVA fiber. Subsequently, a kraft pulp was
subjected to disaggregation, dusting and dehydration, and then beaten. The
kraft pulp thus treated was then mixed with the foregoing PVA fiber at a
ratio of 80:20. The mixture was then subjected to paper making by means of
a cylinder paper machine to prepare an electrolytic paper. The
electrolytic paper thus prepared was then cut to provide a separator. A
cathode foil and an anode foil which has a withstand voltage of 750 V were
then wound with the foregoing separator provided interposed therebetween
to prepare a 500 V-10 .mu.F capacitor element as shown in FIG. 4.
Subsequently, an electrolytic solution comprising 100 parts of ethylene
glycol, 15 parts of ammonium 1,7-octanedicarboxylate and 3.5 parts of
boric acid was prepared. The capacitor element thus prepared was
impregnated with the foregoing electrolytic solution, inserted into an
aluminum case which was then hermetically sealed with a rubber member, and
then subjected to reformation at 550 V under heating to prepare an
aluminum electrolytic capacitor.
EXAMPLE 11
An aluminum electrolytic capacitor was prepared in the same manner as in
Example 10 except that as the electrolytic solution there was used one
comprising 100 parts of ethylene glycol, 15 parts of ammonium
1,6-decanedicarboxylate and 3.5 parts of boric acid.
EXAMPLE 12
An aluminum electrolytic capacitor was prepared in the same manner as in
Example 10 except that as the electrolytic solution there was used one
comprising 100 parts of ethylene glycol, 10 parts of boric acid and 1 part
of ammonium 1,6-decanedicarboxylate into which ammonium gas had been
bubbled.
COMPARATIVE EXAMPLE 9
An aluminum electrolytic capacitor was prepared in the same manner as in
Example 8 except that as the fiber to be mixed in the separator there was
used an ordinary vinylon. The vinylon used is called vinylon staple
obtained by a process which comprises spinning a yarn from an aqueous
solution of PVA in a sodium sulfate solution, and then subjecting the yarn
to heat treatment, drawing and acetalation to form fibers.
COMPARATIVE EXAMPLE 10
An aluminum electrolytic capacitor was prepared in the same manner as in
Example 8 except that as the fiber to be mixed in the separator there was
used a fiber formed by wet spinning process. This fiber was obtained by a
process which comprises spinning a yarn from an aqueous solution of PVA in
a sodium sulfate solution in the same manner as vinylon staple, and then
subjecting the yarn to wet heat drawing in a high temperature aqueous
solution of Glauber's salt, heat drawing and heat treatment to form
fibers.
COMPARATIVE EXAMPLE 11
An aluminum electrolytic capacitor was prepared in the same manner as in
Example 8 except that as the fiber to be mixed in the separator there was
used a fiber formed by an ordinary dry spinning process. This fiber was
obtained by a process which comprises spinning a yarn from an aqueous
solution of PVA in hot air, and then subjecting the yarn to dry heat
drawing and heat treatment.
COMPARATIVE EXAMPLE 12
An aluminum electrolytic capacitor was prepared in the same manner as in
Example 10 except that as the electrolytic solution there was used one
comprising 100 parts of ethylene glycol and 15 parts of ammonium
1,7-octanedicarboxylate.
COMPARATIVE EXAMPLE 13
An aluminum electrolytic capacitor was prepared in the same manner as in
Example 10 except that as the electrolytic solution there was used one
comprising 100 parts of ethylene glycol and 30 parts of boric acid into
which ammonia gas had been injected.
CONVENTIONAL EXAMPLE 2
An aluminum electrolytic capacitor was prepared in the same manner as in
Example 8 except that as the separator there was used an ordinary hemp
paper free of PVA fibers.
CONVENTIONAL EXAMPLE 3
An aluminum electrolytic capacitor was prepared in the same manner as in
Example 8 except that as the separator there was used an ordinary hemp
paper free of PVA fibers and PVA (saponification degree: 98.5 mol-%;
polymerization degree: 330) was incorporated in the electrolytic solution
in an amount of 3%.
CONVENTIONAL EXAMPLE 4
An aluminum electrolytic capacitor was prepared in the same manner as in
Example 8 except that as the separator there was used an ordinary hemp
paper free of PVA fibers and as the electrolytic solution there was used
one comprising 100 parts of ethylene glycol and 5 parts of ammonium
1,6-decanedicarboxylate.
CONVENTIONAL EXAMPLE 5
An aluminum electrolytic capacitor was prepared in the same manner as in
Example 10 except that as the separator there was used an ordinary
separator and as the electrolytic solution there was used one comprising
100 parts of ethylene glycol and 5 parts of ammonium
1,6-decanedicarboxylate.
The aluminum electrolytic capacitors of Examples 8 and 9, Comparative
Examples 9 to 11 and Conventional Examples 2 to 4 were each subjected to
high-temperature load test at 500 V and 105.degree. C. for 2,000 hours.
The results of the high-temperature load test are set forth in Table 5.
Further, the aluminum electrolytic capacitors of Examples 10 to 12,
Comparative Examples 12 and 13 and Conventional Example 5 were each
subjected to high-temperature load test at 500 V and 105.degree. C. for
1,000 hours. The results of the high-temperature load test are set forth
in Table 6. For these tests, 20 pieces of the electrolytic capacitor were
used for each example. In order to determine various properties, the value
of 20 pieces were averaged.
TABLE 5
______________________________________
Initial properties
After 105.degree. C.-2000 hrs
Capacitance % Capacitance
(.mu.F) tan .delta. change tan .delta.
______________________________________
Example 8 10.05 0.026 -0.1 0.038
Example 9 10.01 0.025 -0.1 0.035
Comparative
Shortcircuited
-- --
Example 9 during reformation
Comparative Shortcircuited -- --
Example 10 during reformation
Comparative
10.08 0.026 Shortcircuited
Example 11
Conventional
Shortcircuited
-- --
Example 2 during reformation
Conventional Shortcircuited -- --
Example 3 during reformation
Conventional
10.06 0.051 Shortcircuited
Example 4
______________________________________
TABLE 6
______________________________________
Initial properties
After 105.degree. C.-2000 hrs
Capacitance % Capacitance
(.mu.F) tan .delta. change tan .delta.
______________________________________
Example 10 10.00 0.018 -0.2 0.023
Example 11 10.04 0.021 -0.4 0.025
Example 12 10.08 0.024 -0.4 0.026
Comparative
Shortcircuited
-- --
Example 12 during reformation
Comparative
9.84 0.091 0.1 0.103
Example 13
Conventional
9.96 0.085 Short circuited
Example 5
______________________________________
It can be seen in Table 5 that the electrolytic capacitor of Comparative
Example 9 comprising a separator having an ordinary vinylon mixed therein
and the electrolytic capacitor of Comparative Example 10 comprising a
separator having a fiber formed by wet spinning process mixed therein show
shortcircuiting during reformation as in Conventional Examples 2 and 3
comprising a separator made of hemp paper and thus exhibit no improvement
in withstand voltage.
The electrolytic capacitor of Comparative Example 11 comprising a separator
having a fiber formed by dry spinning process mixed therein and the
electrolytic capacitor of Conventional Example 4 comprising an ordinary
electrolytic paper and an electrolytic solution having 5 parts of
1,6-decanedicarboxylic acid incorporated therein as a solute show no
shortcircuiting during reformation but show shortcircuiting during
105.degree. C.-2000 hr load test and thus exhibit an insufficient
withstand voltage.
The electrolytic capacitors of Conventional Examples 2 and 3 exhibit a
reformable voltage of 400 V and 450 V, respectively, and a maximum
allowable voltage of 350 V and 400 V, respectively. The electrolytic
solutions of Conventional Examples 2 and 3 exhibit an electrical
conductivity of 2.3 mS/cm and 2.0 mS/cm, respectively. The electrolytic
capacitors which had been subjected to reformation at the respective
reformation voltage exhibited a tan .delta. value of 0.025 and 0.030,
respectively.
On the contrary, the electrolytic capacitor of Example 8 comprising a
separator having PVA fiber made of PVA having a saponification degree of
80 mol-% mixed therein and the electrolytic capacitor of Example 9
comprising a separator having PVA fiber made of PVA having a
saponification degree of 98 mol-% mixed therein maintain good properties
even after 2,000 hours of 105.degree. C. load test. In other words, these
electrolytic capacitors exhibit a maximum allowable voltage of not less
than 500 V. As compared with those of Conventional Examples 2 and 3, the
electrolytic capacitors of these examples show a withstand voltage rise of
not less than 100 V. In Example 8, a voltage was applied at a constant
current. As a result, it was found that the voltage reached 650 V, which
is the withstand voltage of the anode foil. As mentioned above, the
electrolytic capacitors of the present invention exhibit a drastically
increased withstand voltage.
The initial tan .delta. value of these electrolytic capacitors remain the
same as that of the electrolytic capacitor of Conventional Example 2
comprising an ordinary electrolytic paper and an ordinary electrolytic
solution and are lower than that of the electrolytic capacitor of
Conventional Example 3 comprising an ordinary electrolytic paper and an
electrolytic solution comprising PVA dissolved therein. Further, the
initial tan .delta. value of these electrolytic capacitors are each about
half that of the electrolytic capacitor of Conventional Example 4
comprising 5 parts of 1, 6-decanedicarboxylic acid as a solute. Thus, the
electrolytic capacitors according to the present invention remain the same
as the conventional middle and high voltage electrolytic capacitors in
dielectric loss.
It can be seen in Table 6 that the electrolytic capacitor of Comparative
Example 12 comprising an electrolytic solution free of boric acid shows
shortcircuiting during reformation and the electrolytic capacitor of
Conventional Example 5 comprising an ordinary separator and an
electrolytic solution containing 1, 6-decanedicarboxylic acid as a solute
shows shortcircuiting during the high-temperature load test. Thus, these
examples cannot provide a withstand voltage that allows the preparation of
an electrolytic capacitor having a rated voltage of 500 V. The
electrolytic capacitor of Comparative Example 13 comprising boric acid
alone as a solute exhibits a raised tan .delta. value at the initial stage
and after 2,000 hours of high temperature load. On the contrary, the
initial tan .delta. value of the electrolytic capacitors of Examples 10 to
12 are each about 1/5 to 1/2 of that of the electrolytic capacitors of
Comparative Example 3 and Conventional Example 5. The electrolytic
capacitors of Examples 10 to 12 show little change in tan .delta. even
after 2,000 hours of 105.degree. C. load test. Thus, the synergistic
effect obtained by the high withstand voltage of the electrolytic
capacitor of the present invention and the electrolytic solution having a
high sparking voltage and electrical conductivity makes it possible to
obtain a high withstand voltage while maintaining a low dielectric loss
and hence realize an electrolytic capacitor having a rated voltage of 500
V.
Subsequently, the aluminum electrolytic capacitors of Examples 8 to 12 and
Comparative Example 11 were each subjected to overvoltage test at 550 V
and 600 V at 105.degree. C. for 50 hours. The results of the test are set
forth in Table 7, For this test, 20 pieces of the electrolytic capacitor
were used for each example. The number of pieces showing shortcircuiting
is set forth in Table 7.
TABLE 7
______________________________________
After 600 V-50 hrs
After 550 V-50 hrs Number of pieces
Number of pieces showing showing
Example No. shortcircuiting shortcircuiting
______________________________________
Example 8 0 2
Example 9 0 0
Example 10 0 0
Example 11 0 0
Example 12 0 0
Comparative 20 --
Example 11
______________________________________
It can be seen in Table 7 that all the pieces of the electrolytic capacitor
of Comparative Example 11 comprising a separator having a fiber formed by
ordinary dry spinning method mixed therein show shortcircuiting during 550
V-50 hr overvoltage test. On the contrary, the electrolytic capacitor of
Example 8 comprising a separator having a PVA fiber of the present
invention of PVA having a saponification degree of 80 mol-% mixed therein
and the electrolytic capacitors of Examples 9 to 12 comprising a separator
having a PVA fiber of the present invention of PVA having a saponification
degree of 98 mol-% mixed therein show no shortcircuiting and thus exhibit
a good overvoltage resistance. Further, the electrolytic capacitors of
Examples 9 to 12 comprising PVA having a saponification degree of 98 mol-%
show no shortcircuiting even after 50 hours of 600 V load and thus exhibit
an even higher overvoltage resistance.
Embodiments of the electrolytic capacitor according to the third aspect of
the present invention comprising PVA attached to both end faces of the
capacitor element and an electrolytic solution containing dicarboxylic
acids having side chains and boric acid will be described hereinafter.
EXAMPLE 13
As shown in FIG. 4, an anode foil 14 having an oxide layer formed on the
surface of a roughened aluminum foil and a cathode foil 15 made of
aluminum were wound with a separator 16 made of paper or the like provided
interposed therebetween to prepare a capacitor element 1. The capacitor
element 1 was then impregnated with a driving electrolytic solution
comprising 100 parts of ethylene glycol, 15 parts of ammonium
1,7-octanedicarboxylate and 3 parts of boric acid. 1. A PVA powder was
then attached to the end faces 12 and 13 of the capacitor element as shown
in FIG. 1. The capacitor element thus prepared was inserted into a
closed-end cylindrical outer case 2 which was then hermetically sealed
with a sealing member, subjected to heat treatment at 85.degree. C., and
then subjected to reformation at 550 V to prepare an aluminum electrolytic
capacitor. The rated voltage and capacitance of the aluminum electrolytic
capacitor thus prepared were 500 V and 10 .mu.F, respectively.
EXAMPLE 14
In Example 13, a PVA powder was attached to both end faces 12 and 13 of a
capacitor element impregnated with an electrolytic solution. In the
present example, PVA was attached to only the end face 12 of a capacitor
element impregnated with an electrolytic solution. The electrolytic
capacitor was then subjected to heat treatment in such an arrangement that
it was positioned as shown in FIG. 2.
EXAMPLE 15
In Example 13, a PVA powder was attached to both end faces 12 and 13 of a
capacitor element impregnated with an electrolytic solution. In the
present example, PVA was placed on the inner bottom 21 of the outer case
to prepare an aluminum electrolytic capacitor. Heat treatment was effected
in such an arrangement that the bottom of the capacitor faces upward,
i.e., the position of the capacitor is reversed from that of FIG. 3.
COMPARATIVE EXAMPLE 14
An aluminum electrolytic capacitor was prepared in the same manner as in
Example 13 except that as the electrolytic solution there was used one
comprising 100 parts of ethylene glycol and 15 parts of ammonium
1,7-octanedicarboxylic acid.
CONVENTIONAL EXAMPLE 6
An aluminum electrolytic capacitor was prepared in the same manner as in
Example 13 except that no PVA was used.
These aluminum electrolytic capacitors were then subjected to
high-temperature load test. The load test was conducted at an applied
voltage of 500 V and a temperature of 105.degree. C. for 1,000 hours. The
results of the load test are set forth in Table 8.
TABLE 8
______________________________________
Initial properties
After 105.degree. C.-1000 hrs
Capacitance % Capacitance
(.mu.F) tan .delta. change tan .delta.
______________________________________
Example 13 9.82 0.025 -0.2 0.036
Example 14 9.76 0.024 -0.2 0.036
Example 15 9.91 0.024 -0.4 0.037
Comparative
Shortcircuited
-- --
Example 14 during reformation
Conventional Shortcircuited -- --
Example 6 during reformation
______________________________________
It can be seen in Table 8 that the electrolytic capacitor of Conventional
Example 6 shows shortcircuiting during reformation and the electrolytic
capacitor of Comparative Example 14 comprising an electrolytic solution
free of boric acid shows shortcircuiting during reformation and thus
exhibits no improvement of withstand voltage. On the contrary, the
electrolytic capacitors of Examples 13 to 15 maintain good properties even
after 2,000 hours of 105.degree. C. load. In other words, by the
synergistic effect obtained by the improvement of withstand voltage and
the high sparking voltage and electrical conductivity of the electrolytic
solution, the electrolytic capacitors of the present invention exhibit a
high withstand voltage while maintaining a low dielectric loss. Thus,
electrolytic capacitors having a rated voltage of 500 V can be realized.
Subsequently, the aluminum electrolytic capacitors of Examples 13 to 15
were each subjected to overvoltage test at 550 V and 600 V at 105.degree.
C. for 50 hours. The results of the test are set forth in Table 9.
TABLE 9
______________________________________
After 600 V-50 hrs
After 550 V-50 hrs Number of pieces
Number of pieces showing showing
Example No. shortcircuiting shortcircuiting
______________________________________
Example 13 0 0
Example 14 0 0
Example 15 0 0
______________________________________
It can be seen in Table 9 that the electrolytic capacitors of Examples 13
to 15 show no shortcircuiting during overvoltage test and thus exhibit a
good overvoltage resistance.
Embodiments of the electrolytic capacitor according to the first to third
aspects of the present invention comprising an electrolytic solution
containing straight-chain dicarboxylic acids and boric acid will be
described hereinafter.
EXAMPLE 16
An aqueous solution having PVA (saponification degree: 98 mol-%;
polymerization degree: 1,700) dissolved therein in an amount of 35% was
extruded into hot air through a spinneret to form a filament which was
then wound to prepare a PVA fiber. Subsequently, a kraft pulp was
subjected to disaggregation, dusting and dehydration, and then beaten. The
kraft pulp thus treated was then mixed with the foregoing PVA fiber at a
ratio of 80:20. The mixture was then subjected to paper making by means of
a cylinder paper machine to prepare an electrolytic paper. The
electrolytic paper thus prepared was then cut to provide a separator. A
cathode foil and an anode foil which has a withstand voltage of 650 V were
then wound with the foregoing separator provided interposed therebetween
to prepare a capacitor element as shown in FIG. 4. Subsequently, an
electrolytic solution comprising 100 parts of ethylene glycol, 10 parts of
ammonium adipate and 3 parts of boric acid was prepared. The capacitor
element thus prepared was impregnated with the foregoing electrolytic
solution, inserted into an aluminum case which was then hermetically
sealed with a rubber member, and then subjected to reformation at 450 V
under heating to prepare an aluminum electrolytic capacitor having a rated
voltage of 400 V and a rated capacitance of 10 .mu.F.
EXAMPLE 17
As shown in FIG. 4, an anode foil 14 having an oxide layer formed on the
surface of a roughened aluminum foil and a cathode foil 15 made of
aluminum were wound with a separator 12 made of paper or the like provided
interposed therebetween to prepare a capacitor element 1. The capacitor
element 1 was then impregnated with a driving electrolytic solution
comprising 100 parts of ethylene glycol, 10 parts of ammonium adipate and
3 parts of boric acid. A PVA powder was then applied to the end faces 12
and 13 of the capacitor element to form a PVA layer thereof as shown in
FIG. 1. The capacitor element thus prepared was inserted into a closed-end
cylindrical outer case 2 which was then hermetically sealed with a sealing
member, heated, and then subjected to reformation at 450 V to prepare an
aluminum electrolytic capacitor. The rated voltage and capacitance of the
aluminum electrolytic capacitor thus prepared were 400 V and 10 .mu.F,
respectively.
EXAMPLE 18
An aqueous solution having PVA (saponification degree: 96 mol-%;
polymerization degree: 1,700) dissolved therein in an amount of 20% was
applied to a separator (kraft paper; density: 0.75 g/cm.sup.3 ; thickness:
50 .mu.m) by means of a comma reverse type coating machine, and then
heated and dried to obtain a separator having PVA attached thereto. The
attached amount of PVA was 5 g/m.sup.2. A cathode foil and an anode foil
which has pits with a diameter of not less than 0.1 .mu.m formed thereon
were then wound with the foregoing separator provided interposed
therebetween to prepare a 400V-10 .mu.F capacitor element. Separately, an
electrolytic solution comprising 100 parts of ethylene glycol, 10 parts of
ammonium adipate and 3 parts of boric acid was prepared. The capacitor
element thus prepared was impregnated with the foregoing electrolytic
solution, inserted into an aluminum case which was then hermetically
sealed with a rubber member, and then subjected to reformation at 450 V
under heating while the electrolytic solution was being gelled to prepare
an aluminum electrolytic capacitor.
COMPARATIVE EXAMPLE 15
An aluminum electrolytic capacitor was prepared in the same manner as in
Example 16 except that as the electrolytic solution there was used one
comprising 100 parts of ethylene glycol and 10 parts of ammonium adipate.
COMPARATIVE EXAMPLE 16
An aluminum electrolytic capacitor was prepared in the same manner as in
Example 16 except that an ordinary separator was used.
COMPARATIVE EXAMPLE 17
An aluminum electrolytic capacitor was prepared in the same manner as in
Example 18 except that as the electrolytic solution there was used one
comprising 100 parts of ethylene glycol and 10 parts of ammonium adipate.
COMPARATIVE EXAMPLE 18
An aluminum electrolytic capacitor was prepared in the same manner as in
Example 18 except that an ordinary separator was used.
CONVENTIONAL EXAMPLE 7
An aluminum electrolytic capacitor was prepared in the same manner as in
Example 16 except that as the separator there was used an ordinary
separator and as the electrolytic solution there was used one comprising
100 parts of ethylene glycol and 15 parts of ammonium
1,7-octanedicarboxylate.
CONVENTIONAL EXAMPLE 8
An aluminum electrolytic capacitor was prepared in the same manner as in
Example 18 except that as the separator there was used an ordinary
separator and as the electrolytic solution there was used one comprising
100 parts of ethylene glycol, 15 parts of ammonium
1,7-octanedicarboxylate, 3.5 parts of boric acid and 3 parts of PVA.
These aluminum electrolytic capacitors were each subjected to
high-temperature load test. The load test was effected at an applied
voltage of 400 V at 105.degree. C. for 1,000 hours for Examples 16 and 17,
Comparative Examples 15 and 16 and Conventional Example 7. The results of
the test are set forth in Table 10. For Example 18, Comparative Examples
17 and 18 and Conventional Example 8, the load test was conducted at an
applied voltage of 400 V at 105.degree. C. for 2,000 hours. The results of
the test are set forth in Table 11. For this test, 20 pieces of the
electrolytic capacitor were used for each example. In order to determine
various properties, the values of 20 pieces were averaged.
TABLE 10
______________________________________
Initial properties
After 105.degree. C.-1000 hrs
Capacitance % Capacitance
(.mu.F) tan .delta. change tan .delta.
______________________________________
Example 16 10.35 0.013 -2.5 0.017
Example 17 10.24 0.015 -2.4 0.018
Comparative
Shortcircuited
-- --
Example 15 during reformation
Comparative Shortcircuited -- --
Example 16 during reformation
Conventional
10.03 0.025 -1.5 0.030
Example 7
______________________________________
TABLE 11
______________________________________
Initial properties
After 105.degree. C.-2000 hrs
Capacitance % Capacitance
(.mu.F) tan .delta. change tan .delta.
______________________________________
Example 18 10.18 0.015 -2.4 0.018
Comparative
Shortcircuited
-- --
Example 17 during reformation
Comparative Shortcircuited -- --
Example 18 during reformation
Conventional
10.11 0.033 -1.9 0.036
Example 8
______________________________________
It can be seen in Table 10 that the electrolytic capacitor of Comparative
Example 15 comprising an electrolytic solution free of boric acid and the
electrolytic capacitor of Comparative Example 16 comprising an ordinary
separator show shortcircuiting during reformation. Thus, these examples
cannot provide a withstand voltage that allows the preparation of an
electrolytic capacitor having a rated voltage of 400 V. The electrolytic
capacitor of Conventional Example 7 comprising an electrolytic solution
containing boric acid which is an electrolytic solution for conventional
400 V electrolytic capacitor using ammonium 1,7-octanedicarboxylate
exhibits a high tan .delta. value at the initial stage and after
high-temperature load test. On the contrary, the tan .delta. value of the
electrolytic capacitors of Examples 16 and 17 are about half that of the
conventional example at the initial stage and after the load test. Thus,
these electrolytic capacitors exhibit a reduced dielectric loss.
It can be seen in Table 11 that the electrolytic capacitor of Comparative
Example 17 comprising an electrolytic solution free of boric acid and the
electrolytic capacitor of Comparative Example 18 comprising an ordinary
separator show shortcircuiting during reformation. On the contrary, the
tan .delta. value of the electrolytic capacitor of Example 18 is about
half that of Conventional Example 8 at the initial stage and after the
high-temperature load test. In other words, the synergistic effect
obtained by the improvement of withstand voltage of the electrolytic
capacitor of the present invention and the high electrical conductivity of
the electrolytic solution makes it possible to obtain a 400 V aluminum
electrolytic capacitor having a low dielectric loss.
In order to evaluate overvoltage resistance, 20 pieces of aluminum
electrolytic capacitor were prepared for each of Examples 16 to 18 and
Conventional Examples 7 and 8. The overvoltage test was conducted at an
applied voltage of 450 V and 500 V at 105.degree. C. for 50 hours. The
results of the test are set forth in Table 12.
TABLE 12
______________________________________
After 450 V-50 hrs
After 500 V-50 hrs
Number of pieces Number of pieces
showing showing
Example No. shortcircuiting shortcircuiting
______________________________________
Example 16 0 0
Example 17 0 0
Example 18 0 0
Conventional 3 8
Example 7
Conventional 3 20
Example 8
______________________________________
It can be seen in Table 12 that the electrolytic capacitors of Examples 16
to 18 show no shortcircuiting during 450 V-50 hour and 500 V-50 hour
overvoltage tests while the electrolytic capacitor of Conventional Example
7 shows shortcircuiting during these overvoltage tests. Thus, the
electrolytic capacitors of the present invention exhibit an improved
overvoltage resistance.
Embodiments of the electrolytic capacitor according to the first and second
aspects of the present invention comprising an electrolytic solution
containing other straight-chain dicarboxylic acids and boric acid will be
described hereinafter.
EXAMPLE 19
An aluminum electrolytic capacitor having a rated voltage of 450 V and a
rated capacitance of 10 .mu.m was prepared in the same manner as in
Example 16 except that as the anode foil there was used one having a
withstand voltage of 700 V, as the electrolytic solution there was used
one comprising 100 parts of ethylene glycol, 10 parts of ammonium benzoate
and 3 parts of boric acid, and the electrolytic capacitor was subjected to
reformation at 500 V.
EXAMPLE 20
An aluminum electrolytic capacitor was prepared in the same manner as in
Example 18 except that a 450 V-10 .mu.F capacitor element was used, an
electrolytic solution comprising 100 parts of ethylene glycol, 10 parts of
ammonium benzoate and 3 parts of boric acid was used, and the electrolytic
capacitor was subjected to reformation at 500 V.
COMPARATIVE EXAMPLE 19
An aluminum electrolytic capacitor was prepared in the same manner as in
Example 19 except that as the electrolytic solution there was used one
comprising 100 parts of ethylene glycol and 10 parts of ammonium benzoate.
COMPARATIVE EXAMPLE 20
An aluminum electrolytic capacitor was prepared in the same manner as in
Example 19 except that an ordinary separator was used.
COMPARATIVE EXAMPLE 21
An aluminum electrolytic capacitor was prepared in the same manner as in
Example 20 except that an ordinary separator was used.
CONVENTIONAL EXAMPLE 9
An aluminum electrolytic capacitor was prepared in the same manner as in
Example 19 except that as the separator there was used an ordinary
separator and as the electrolytic solution there was used one comprising
100 parts of ethylene glycol, 15 parts of ammonium 1,6-decanedicarboxylate
and 3 parts of boric acid.
CONVENTIONAL EXAMPLE 10
An aluminum electrolytic capacitor was prepared in the same manner as in
Example 20 except that as the separator there was used an ordinary
separator and as the electrolytic solution there was used one comprising
100 parts of ethylene glycol, 15 parts of ammonium
1,6-octanedicarboxylate, 10 parts of boric acid and 3 parts of PVA.
These aluminum electrolytic capacitors were each then subjected to
high-temperature load test. The load test was effected at an applied
voltage of 450 V at 105.degree. C. for 1,000 hours for Example 19,
Comparative Examples 19 and 20 and Conventional Example 9. For Example 20,
Comparative Example 21 and Conventional Example 10, the load test was
conducted at an applied voltage of 450 V at 105.degree. C. for 2,000
hours. The results of the test are set forth in Tables 13 and 14.
TABLE 13
______________________________________
Initial properties
After 105.degree. C.-1000 hrs
Capacitance % Capacitance
Example No. (.mu.F) tan .delta. change tan .delta.
______________________________________
Example 19 10.21 0.010 -2.3 0.015
Comparative
Shortcircuited
-- --
Example 19 during reformation
Comparative Shortcircuited -- --
Example 20 during reformation
Conventional
10.01 0.029 -1.8 0.031
Example 9
______________________________________
TABLE 14
______________________________________
Initial properties
After 105.degree. C.-2000 hrs
Capacitance % Capacitance
Example No. (.mu.F) tan .delta. change tan .delta.
______________________________________
Example 20 10.33 0.017 0.1 0.021
Comparative
Shortcircuited
-- --
Example 21 during reformation
Conventional
10.00 0.040 -2.1 0.044
Example 10
______________________________________
It can be seen in Table 13 that the electrolytic capacitor of Comparative
Example 19 comprising an electrolytic solution free of boric acid and the
electrolytic capacitor of Comparative Example 20 comprising an ordinary
separator show shortcircuiting during reformation. Thus, these examples
cannot provide a withstand voltage that allows the preparation of an
electrolytic capacitor having a rated voltage of 450 V. The electrolytic
capacitor of Conventional Example 9 comprising an electrolytic solution
containing 1,6-decanedicarboxylic acid which is an electrolytic solution
for conventional 450 V electrolytic capacitor exhibits a high tan .delta.
value at the initial stage and after high-temperature load test. On the
contrary, the tan .delta. value of the electrolytic capacitor of Example
19 is about one third of that of Conventional Example 9 at the initial
stage and after the load test.
It can be seen in Table 14 that the electrolytic capacitor of Comparative
Example 21 comprising an ordinary separator shows shortcircuiting during
reformation, demonstrating the effect of the separator of the present
invention. The tan .delta. value of the electrolytic capacitor of Example
20 is half that of the electrolytic capacitor of Conventional Example 10
at the initial stage and after high-temperature load test. Thus, the
electrolytic capacitor of Example 20 is an aluminum electrolytic capacitor
having a low dielectric loss. As mentioned above, the synergistic effect
obtained by the improvement of withstand voltage of the present invention
and the high electrical conductivity of the electrolytic solution makes it
possible to realize an aluminum electrolytic capacitor for middle and high
voltage having an unprecedentedly low dielectric loss, i.e., tan .delta.
value reduced to 1/3 to 1/2 of the conventional example.
In order to evaluate overvoltage resistance, 20 pieces of aluminum
electrolytic capacitor were prepared for each of Examples 19 and 20 and
Conventional Examples 9 and 10. The overvoltage test was conducted at an
applied voltage of 500 V and 550 V at 105.degree. C. for 50 hours. The
results of the test are set forth in Table 15.
TABLE 15
______________________________________
After 500 V-50 hrs
After 550 V-50 hrs
Number of pieces Number of pieces
showing showing
Example No. shortcircuiting shortcircuiting
______________________________________
Example 19 0 0
Example 20 0 0
Conventional 4 10
Example 9
Conventional 4 10
Example 10
______________________________________
It can be seen in Table 15 that the electrolytic capacitors of Examples 19
and 20 show no shortcircuiting during 500 V-50 hour and 550 V-50 hour
overvoltage tests while the electrolytic capacitors of Conventional
Examples 9 and 10 show shortcircuiting during these overvoltage tests.
Thus, the electrolytic capacitors of the present invention exhibit an
improved overvoltage resistance.
The electrolytic capacitor according to the first aspect of the present
invention comprises a capacitor element formed by winding an anode foil
having pits with a diameter of not less than 0.1 .mu.m formed on the
surface thereof and a cathode foil with a separator provided interposed
therebetween, said separator having been coated with PVA which is then
dried, said capacitor element being in contact with an electrolytic
solution for electrolytic capacitor containing ethylene glycol, whereby
said electrolytic solution is gelled. The electrolytic capacitor according
to the second aspect of the present invention comprises a capacitor
element formed by winding an anode foil and a cathode foil with a
separator provided interposed therebetween, said separator having been
prepared by mixing filament fibers formed by extruding PVA solution into a
gas, said capacitor element being impregnated with an electrolytic
solution. The electrolytic capacitor according to the third aspect of the
present invention is prepared by a process which comprises impregnating a
capacitor element formed by winding an anode foil, a cathode foil and a
separator with a driving electrolytic solution, inserting said capacitor
element into an outer case, sealing the opening of said outer case with a
sealing member, and then subjecting said anode to reformation, wherein
said driving electrolytic solution contains boric acid and a polyvinyl
alcohol is attached to at least both the upper and lower end faces of said
capacitor element. Proper selection of the form of PVA in the electrolytic
capacitor of the present invention allows PVA dissolved in the
electrolytic solution to effectively act on the electrode foil, making it
possible to improve the withstand voltage and overvoltage resistance
without raising the dielectric loss of the electrolytic capacitor.
Further, if the electrolytic solution contains dicarboxylic acids having
side chains and boric acid, it exhibits a high sparking voltage and a high
electrical conductivity. Therefore, the synergistic effect obtained by
electrolytic capacitor and electrolytic solution makes it possible to
obtain an electrolytic capacitor for middle and high voltage having a
higher withstand voltage and a high overvoltage resistance without
impairing the dielectric loss.
If the electrolytic solution to be used comprises straight-chain aliphatic
dicarboxylic acids and boric acid, it exhibits a high electrical
conductivity, and the resulting synergistic effect obtained by
electrolytic capacitor and electrolytic solution makes it possible to
obtain an electrolytic capacitor having a withstand voltage suitable for
use in middle and high voltage range and a low dielectric loss. Further, a
high overvoltage resistance can be obtained.
While the invention has been described in detail and with reference to
specific embodiments thereof, it will be apparent to one skilled in the
art that various changes and modifications can be made therein without
departing from the spirit and scope thereof.
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